Fluid pump, a fluid-transfer plate and an inductive sensor for a fluid pump

ABSTRACT

The present invention relates to a fluid pump and a fluid-transfer plate and a sensor for a fluid pump, particularly applicable to linear compressors, for detecting the position of the respective piston and preventing the latter from colliding with the fluid-transfer plate upon variations in the compressor operation conditions, or even variations in the feed voltage. The objectives of the present invention are achieved by means of a fluid pump ( 1 ) comprising a piston ( 2 ) that is axially displaceable within a cylinder ( 3 ), the cylinder ( 3 ) comprising a cylinder closing fluid-transfer plate ( 40 ), the piston ( 2 ) being displaced toward the fluid-transfer plate ( 40 ) and capturing a gas or fluid from a low-pressure environment ( 11 ), and the fluid pump ( 11 ) comprising a sensor assembly ( 98 ), which includes an inductive sensor ( 8 ) associated with the fluid-transfer plate ( 40 ). The objectives of the present invention are also achieved by means of a fluid-transfer plate ( 40 ) particularly applicable to a fluid pump ( 1 ) and that comprises a valve plate ( 4 ) provided with a though-bore ( 10 ) for associating a protector ( 9 ) that cooperates with the cavity ( 10 ), the protector ( 9 ) comprising at least one sensor cavity ( 8 ′) for associating an inductive sensor ( 8 ). An inductive sensor ( 8 ) is also foreseen, which is applicable to the fluid pump ( 1 ).

The present invention relates to a fluid pump, a fluid-transfer plateand a sensor for a fluid pump, particularly applicable to linearcompressors, for detecting the position of the respective piston andpreventing the latter from colliding with the fluid-transfer plate uponvariations in the compressor operation conditions, or even variations inthe feed voltage.

DESCRIPTION OF THE PRIOR ART

A linear compressor basically comprises an axially displaceable pistonin a bored-through body, usually a cylinder, the function of the pistonbeing to compress the gas used in the cooling cycle. The gas-compressionmechanism takes place by virtue of the axial movement of the piston,suction and discharge valves being positioned at the end of the pistonstroke, which adjust the inlet and outlet of the gas in the cylinder.The piston is actuated by an actuator, which is formed by a support anda magnet, which is actuated by a coil, this assembly being furtheractuated by a helical spring, forming a resonant assembly of thecompressor.

The resonant assembly actuated by the linear motor has the function ofdeveloping a linear alternating movement, causing the movement of thepiston inside the cylinder to exert a compression action on the gasadmitted by the suction valve up to the point at which it may bedischarged to the high-pressure side through the discharge valve.

Variations in the compressor operation conditions, or even variations inthe feed voltage, may cause the resonant assembly to be displaced morethan necessary, thus leading the piston to collide at the end of itsstroke, which causes noises and even damages to the compressor.Therefore, a means of controlling the piston movement is necessary.

Various solutions for controlling the piston movement have already beenproposed, such as that disclosed in document EP 0 398 012, whichdescribes a sensor locate at the end of the stroke of an actuatorpiston. Such an actuator is built from a disc manufactured with aconducting material in order to enable one to determine the distancebetween the piston and the end of the stroke of the cylinder by means ofa magnetic sensor, in order to prevent collision of the piston at theend of the stroke of the cylinder. One of the drawbacks of this solutionis that the positioning of the sensor as proposed causes it to besubject to the inner pressure of the cylinder, which results in troubleswith the tightness of the equipment, besides complications in theelectric connections of the sensor, since the latter is subjected tohigh-compression areas, and this may cause malfunction thereof as timepasses.

Another solution of the prior art is disclosed in document U.S. Pat. No.4,924,675, which describes a linear compressor provided with a magneticsensor that detects the position of the piston in its stroke by means ofthe magnetic flow created between the sensor and a magnet existing inthe piston. The positioning of the sensor in the external structure ofthe piston stroke in the cylinder causes this existing wall between thesensor and the piston to be an obstacle for the passage of the magneticflow that is necessary to detect the piston stroke.

A further solution of the prior art is described in document DE 3246731,which discloses a sensor positioned at the end of the piston stroke, butprotuberant with respect to the cylinder structure. With thisconstruction, the piston may collide at the end of its stroke, and theposition sensor may be broken or damaged.

Another solution of the prior art is described in document U.S. Pat. No.6,084,320, which discloses a position sensor positioned at the beginningof the piston stroke and fixed to the piston body. Since in thissolution, the sensor moves together with the piston, the possibility ofthe latter suffering damages due to this movement is great, for whichreason this configuration is litter reliable, besides bringingcomplications while assembling the equipment.

Further solutions are described, for example, in documents U.S. Pat. No.4,471,304, U.S. Pat. No. 5,455,509 and EP 0 271 878, which disclose theposition of the sensor for detecting the piston stroke at the side ofthe cylinder and without adequate protection for them. The drawback inthese cases is the need to provide a magnetic layer on the piston fordetecting its position, which limits the use of piston types in theseconfigurations.

A problem that exists in the prior art is the fact that a sensorprovided on a compressor is subjected to varying pressures, whichoscillate between the minimum pressure of the gas or fluid to becompressed and the maximum pressure of the gas or fluid compressed bythe compressor. This pressure variation may cause tightness problems tothe compressor: (i) since the compressed gas or fluid may leak at theplace of positioning the sensor, and (ii) to the monitoring circuit ofmovement of the compressor piston, since the electric connections of thesensor may be impaired by the high pressures to which the regions wherethe gas or fluid is compressed by the piston are subjected.

Other approaches to the problem are described, for instance, in documentPI 0001404, which discloses a piston-detecting sensor that preventscollision thereof with the cylinder head, provided with an electricprobe cooperating with the control circuit. In this case, the detectionof the proximity of the piston to its stroke end is effected by electriccontact of the piston with the sensor. Although this solution meets therequirements and prevents impact of the piston, this solution usingphysical contact of the sensor with the piston may generate electricnoise, which may interfere with the precision in measurement.

In the face of the drawbacks cited above, the present inventiondiscloses improvements in the area of compressors provided with apiston-position sensor.

OBJECTIVES OF THE INVENTION

One of the objectives of the present invention is to provide a fluidpump, a fluid-transfer plate and an inductive sensor for a fluid pump,in such a configuration that it will enable one to indicate the positionof the piston inside a linear compressor.

Another objective of the present invention is to provide an insulatingprotector for the piston-position inductive sensor of a linearcompressor.

A further objective of the present invention is to provide apiston-position sensor at a location that is subjected to the highpressures of the compressor and that will not suffer mechanicalinterference between the piston and the sensor, by virtue of theisolation of the inductive sensor from the high-pressure environment.

A further objective of the present invention is to provide a sensor thatis inexpensive to manufacture and to implement and, at the same time,has the desired reliability on this type of equipment and that does nothave the drawbacks of the solutions of the prior art.

BRIEF DESCRIPTION OF THE INVENTION

The objectives of the present invention are achieved by means of a fluidpump comprising a piston that is axially displaceable within a cylinder,the cylinder comprising a cylinder closing fluid-transfer plate, thepiston being displaced towards the fluid-transfer plate and capturinggas or is fluid from a low-pressure environment, and the fluid pumpbeing characterized in that it comprises a sensor assembly that includesan inductive sensor associated with the fluid-transfer plate, thefluid-transfer plate comprises a vale plate provided with a through-borefor association of a protector that cooperates with the bore, the sensorbeing positioned in contact with the low-pressure environment.

The objectives of the present invention are also achieved by means of afluid-transfer plate, particularly applicable to a fluid pump andcomprising a valve plate provided with a through-bore for associationwith a protector cooperating with the bore, the protector comprising atleast one as sensor cavity for association with the inductive sensor.

The objectives of the present invention are also achieved by means of aninductive sensor for a fluid pump, particularly applicable for detectingthe piston position, the piston being axially displaceable in acylinder, the fluid pump comprising a valve plate, the inductive sensorbeing installed on a protector, the protector being fixed to athrough-bore provided in the valve plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detail withreference to an embodiment represented in the drawings. The figuresshow:

FIG. 1 is a cross-section view of a fluid pump comprising a sensorprotector according to the object of the present invention;

FIG. 2 is a cross-section view in detail of the position-sensorprotector according to the present invention;

FIG. 3 is a second embodiment of the protector object of the presentinvention; and

FIG. 4 is a cross-section view of a third preferred embodiment of theprotector object of the present invention.

DETAILED DESCRIPTION OF THE FIGURES

As can be seen in FIGS. 1 and 2, a linear compressor 1 (or fluid pump 1)comprises a piston 2 that is axially displaceable within a is cylinder3, the cylinder 3 being usually closed at one of its ends with afluid-transfer plate 40, which in turn comprises a valve plate 4 and anassembly composed of suction valve 4 a and discharge valve 4 b, thesessuction and discharge valve 4 b being associated to the suction openings4 a′ and 4 b′, respectively, which are provided in the valve plate 4.

The compressor 1 is positioned in a low-pressure environment 11, filledwith the gas or fluid that will be compressed by the compressor 1 byvirtue of the axial movement of the piston 2 inside the cylinder 3 (orhigh-pressure environment 11′, when the gas or fluid is compressed) bymeans of the suction valve 4 a and discharge valve 4 b positioned on thetransfer plate 40, which regulate the inlet and outlet of gas or fluidin the cylinder 3. The piston 2 is moved by a motor 66 comprising amagnet 6 that is actuated by a coil 8′, helical spring 7 being mountedagainst the piston 2, so that this spring will always be compressed andform a resonant circuit.

The resonant circuit accounts for the linear movement, causing thepiston 2 to make the desired linear movement and consequently compressthe gas or fluid from the low-pressure environment 11, which goes inthrough the suction valve 4 a, until it can be discharged to thehigh-pressure environment side 11′ through the discharge valve 4 b andled, for instance, to a cooling circuit (not shown).

The operation amplitude of the piston 2 of the compressor 1 is adjustedwith the balance of the power generated by the motor 66 and the powerconsumed by the mechanism in compressing the gas and other losses. Inorder to obtain the best performance of the compressor 1, it isnecessary to operate at an amplitude at which the piston 2 goes as closeas possible to the fluid-transfer plate 40. The operation amplitude ofthe piston 2 should be known with accuracy since, if there are anymistakes, the safety distance for preventing collision of the piston 2with the fluid-transfer plate 40 will have to be longer. This collisionmay damage the compressor 1, depending upon its use and application.Moreover, it should be foreseen that, according to the compressor 1model to which the present invention will be applied, the fluid-transferplate 40 may be configured in different ways. In some models, thesuction valve 4 a projects between the valve plate 4 and the piston 2,as shown in FIG. 2. In this case, the impact will be against the suctionvalve 4 a, and the impact force will be discharged onto the valve plate4 in other manner than in projects of compressor wherein the impact willoccur directly on the cited valve plate 4. In both cases, the impactwill be discharged on the fluid-transfer plate 40, which comprises thevalve plate 4 and the assembly of suction valve 4 a and discharge valve4 b.

A few solutions to this problem have already been discussed in the priorart, but all of them have the already cited drawbacks.

According to a preferred embodiment of the present invention and as canbe seen in FIGS. 1 and 2, in accordance with the teachings of thepresent invention related to the fluid pump, the fluid-transfer plateand the inductive sensor for fluid pumps, one foresees an inductivesensor 8 associated with a protector 9 that, in turn, is associated withthe fluid-transfer plate 40, forming a sensor assembly 98. The inductivesensor we should be positioned so as to emit a magnetic field towardsthe piston 2, that that the later, when approaching, will interfere withsaid magnetic field. In this way, it will be possible to monitor thedistance of the piston with respect to the fluid-transfer plate 40 bymeans of an electronic circuit (not shown, because it is not an objectof the present invention).

In order to make the mounting of the sensor assembly 98 feasible, thefluid-transfer plate 40 should comprise a through-bore 10 for fittingthe protector 9, which will isolate the low-pressure environment 11 fromthe high pressure that occurs inside the cylinder 3 when in phase ofcompression of the gas or fluid.

The protector 9, which is analogous in shape to the bore 10, shouldpreferably be built in cylindrical shape, since thin facilitates theconstruction of the through-bore 10 and, consequently, the manufactureof the compressor 1, which may be manufactured more rapidly and withlower costs.

In this embodiment, the protector 9 has fitting portions 9 c, an openportion 9 a and a closed portion 9 b, forming a substantiallyglass-shaped piece with a sensor cavity 8′ for accommodating a magneticsensor 8. Constructively, the protector 9 is associated in such a way,that the fitting portions 9 c cooperate with the through-bore 10 byinterference, that is to say, the dimensions of the protector 9 shouldbe minimally larger than the through-bore 10, so that it will be firmlyseated on the valve plate 4, thus preventing the leakage of gas or fluidout of the cylinder 3, since this gas or fluid—compressed inside thecylinder 3—may reach high pressures, for example, 30 bar above thepressure in the low-pressure environment 11.

The closed portion 9 b will be aligned with the inner face 9 b′ of thevalve plate 4 and, for this reason, will no invade the bore 10 of thecylinder 3. This will prevent the problems of impact of the sensor withthe piston 2, thus solving the problems of noise measurement of theprior art. At the same time, this configuration allows the inductivesensor 8 to be positioned exactly at the point necessary to preventcollision of the piston 2, since the interpretation of the value of themagnitude measured on the inductive sensor 8 will be directlyproportional to the distance of the piston 2 from the valve plate 4,which facilitate the electronic monitoring of the compressor 1.

The open portion 9 a will leave be sensor cavity 8′ exposed to thelow-pressure environment 11, where the inductive sensor 8 is positionedand fixed preferably against the closed portion 9 b of the protector 9for detecting the distance, and positioned preferably at the end of thepiston 2 stroke. As a material for making the protector 9, one shouldemploy a material that will not block the magnetic flow of the sensor 8too much, for example, stainless steel. Evidently, other compatiblemetallic materials or even polymeric materials may be employed, as longas they meet the mechanical and electric requirements.

With this embodiment, one achieves the objective of keeping the sensor 8protected from the high-pressure environment 11, besides permittingpassage of the electric connections 88 to an electronic circuit (notshow) far coding and interpreting the signals extracted from the sensor1. Further, since the open portion 9 a is positioned in the low-pressureenvironment 11, there will be no interference with the electricconnections 88, which might be affected by the constant fluctuation ofpressure. Another evident advantage resulting from the protector of thepresent invention is that the access to the electric connections 88 willbe facilitated.

Anther advantage resuming from the present invention lies in the factthat the inductive sensor 8 cooperates directly with the material thatconstitutes the piston 2, and it is not necessary for the piston 2 tohave a specific magnetic layer for working with the sensor 8. The lattershould be constituted by a material that interferes with the magneticfield of the sensor 8, as for example, cast iron, aluminum, copper, etc.

The bore 10 and the protector 9 may be foreseen at any other point ofthe cylinder 3, or even in any other configuration of the compressor.Likewise, the position of the sensor 8 within the protector 9 may haveany constructive configuration.

Further as can be seen in FIG. 3, according to a preferred embodiment ofthe present invention, the protector 9 may be fixed between a sealingjoint 3′ (usually present on compressors) and the proper valve plate 4.In this case, it may be not necessary to make a strict control overdimension tolerances of the protector 9 and of the through-bore 10. Inthis embodiment, the valve plate 4 may still comprise recesses 91 forfixing protuberant ends 92, preferably foreseen on the protector 9.

FIG. 4 shows another preferred embodiment of the present invention. Inthis case, the through-bore 10 of the valve plate 4 is closed by aprotecting disc 90 instead of the protector 9.

In this embodiment, with the through-bore 10 being closed, a cavity 10′is formed. In this case, the fixation of the protecting disc 90 iseffected in recesses 93 configured proportionally to the disc 90, theserecesses 93 being provided on the inner face of the cylinder 3. In thiscase, the sensor 8 will be fixed to the back wall of the protecting disc90.

Examples of preferred embodiment having been described, one shouldunderstand that the scope of the present invention embraces otherpossible variations, being limited only by the contents of theaccompanying claims, which include the possible equivalents.

1. A fluid pump comprising: a piston that is axially displaceable withina cylinder; the cylinder comprising a cylinder closing fluid-transferplate; the piston being displaced towards the fluid-transfer plate andcapturing gas or fluid from a low-pressure environment; the fluid pumpcomprising a sensor assembly that includes an inductive sensorassociated with the fluid-transfer plate, the fluid-transfer plate beingprovided with a sealing joint structure; the fluid-transfer platecomprising a valve plate provided with a through-bore for association ofa protector that cooperates with the bore, the sensor being positionedin contact with the low-pressure environment, the valve plate furtherdefining a recess in contact with the low-pressure environment andextending radially outwardly from the through-bore, and the sealingjoint structure being disposed adjacent a surface of the valve plate incontact with the low-pressure environment and defining a generallyplanar portion overlying the recess in the valve plate; and at least aportion of the protector being fixed between the generally planarportion of the sealing joint structure and the recess defined in thevalve plate.
 2. A fluid pump according to claim 1, wherein the protectorcomprises at least one sensor cavity for associating the inductivesensor.
 3. A fluid pump according to claim 2, wherein the inductivesensor emits a magnetic field in the direction of the piston.
 4. A fluidpump according to claim 3, wherein the protector comprises a fittingportion, an open portion, and a closed portion, the fitting portionbeing cooperatively associated with the bore, the closed portionaligning with the inner face of the cylinder, and the open portioncomprising the sensor cavity.
 5. A fluid pump according to claim 4,wherein the valve plate comprises a suction valve associated with alow-pressure environment and a discharge valve associated with ahigh-pressure environment, and still in that the open portion is incontact with the low-pressure environment and the closed portion is incontact with the high-pressure environment.
 6. A fluid pump according toclaim 5, wherein the protector has substantially the same shape as thecavity.
 7. A fluid pump according to claim 1, wherein the protector isbuilt with a material having low magnetic permeability.
 8. A fluid pumpaccording to claim 1, wherein the sensor is fixed to the closed portionof the protector.
 9. A fluid-transfer plate applicable to a fluid pump,comprising: a valve plate provided with a through-bore for associationwith a protector that cooperates with the bore, the protector comprisingat least one sensor cavity configured for receiving an inductive sensortherein, and the valve plate comprising recesses for fixing theprotector, the protector comprising protuberant ends and being fixed tothe valve plate by means of a sealing joint structure, the protuberantends being associable with the recesses in the valve plate and agenerally planar portion of the sealing joint structure, the sealingjoint structure being disposed adjacent the valve plate, wherein atleast a portion of the protuberant ends are disposed between therecesses in the valve plate and the generally planar portion of thesealing joint structure.
 10. A fluid-transfer plate according to claim9, wherein the protector comprises a fitting portion, an open portionand a closed portion, the fitting portion being cooperatively associatedwith the bore, the closed portion aligning with an inner face of thecylinder, and the open portion comprising the sensor cavity.
 11. Aninductive sensor and fluid pump assembly, the assembly comprising: theinductive sensor for detecting the position of a piston in the fluidpump, the piston being axially displaceable in a cylinder, and the fluidpump comprising a fluid-transfer plate, the fluid-transfer platecomprising a valve plate, the inductive sensor being installed on aprotector, the protector being fixed to a through-bore provided in thevalve plate, the valve plate comprising recesses for fixing theprotector, the protector comprising protuberant ends configured suchthat outer surfaces of the protuberant ends are aligned with an outersurface of the valve plate and at least a portion of the protuberantends are disposed between the recesses and a generally planar portion ofa surface of a sealing joint structure that is disposed adjacent theouter surface of the valve plate.
 12. A fluid pump according to claim 1,wherein the valve plate comprises recesses for fixing the protector, theprotector comprising protuberant ends configured such that a surface ofthe protector is aligned with a surface of the valve plate at thelow-pressure environment, the sealing joint structure being configuredsuch that edges of the sealing joint structure are placed substantiallyover the protuberant ends.